The present invention relates to a disk array system and a take-over method for logical units between controllers, and more particularly to a disk array system each of whose controllers has a dedicated cache and a take-over method for logical units between controllers.
A conventional disk array system has a plurality of disks and controllers and a shared cache accessible by each controller.
FIG. 10 is a block diagram showing the structure of a disk array system having a shared cache according to conventional techniques. Conventional techniques will be described with reference to FIG. 10. In FIG. 10, reference numeral 100 represents a large disk array apparatus, reference symbol 200x (x=a, . . . , n) represents controllers, reference numeral 300 represents an expensive shared cache, reference numeral 400 represents a shared memory, reference symbol 500x (x=a, . . . , n) represents disk apparatuses, and reference numeral 600 represents a common bus.
The disk array apparatus 100 shown in FIG. 10 constitutes a disk array system together with other computers (not shown). The disk array apparatus is constituted of a plurality of controllers 200x for controlling disk apparatuses, the shared cache 300 for storing input and output data, the shared memory 400 for storing configuration information or the like, a plurality of disc apparatuses 500x, and the common bus 600 interconnecting these constituent elements. The shared cache 300 and shared memory 400 can be accessed from any controller 200x via the common bus 600. As the shared cache 300, an expensive and large capacity cache is prepared because accesses from all the controllers 200x are concentrated upon this cache. Each controller 200x is assigned a predetermined disk apparatus 500x. The disk array system is connected to a HOST.
With this configuration by conventional techniques, after a disc apparatus 500x under control of one controller 200x is switched to another controller 200x, the destination controller uses input/output data of the source controller stored in the shared cache 300 to change the relation between the disc apparatus 500x and the destination controller 200x. Since configuration information and the like of the disc apparatus necessary for take-over is stored in the shared memory 400, the destination controller refers to the shared memory 400 to start controlling the disk apparatus. The source controller rejects a new access request to the disk apparatus 500x and stops the management of the disk apparatus 500x. With the conventional disk array system having the shared cache, by changing the disk apparatus under the management by some controller, the access amount to logical units of the disc apparatus under the management by the controller can be uniformalized so that load distribution by controllers is possible.
With the above-described conventional techniques, a disk may be mounted or dismounted to change the physical position of the disk to realize load distribution. In this case, the controller stops an access to the subject disk and completely disconnects the disk from the system, and when the disconnected disk is moved to a physically different position, the disk is again recognized to resume the process. With the above-described conventional techniques, a disk may be moved to a different disk apparatus. Therefore, the re-recognized disk is assigned to another new controller to allow load distribution.